Methods and apparatus for expeditiously releasing network resources for a mobile station based on low battery and lost signal conditions

ABSTRACT

Methods and apparatus for expeditiously releasing network resources for a mobile station based on low battery and lost signal conditions are disclosed. The wireless network ( 104 ) receives a power down warning message from the mobile station ( 102 ) indicative of a low battery condition. The wireless network ( 104 ) then identifies whether a lost signal condition exists with the mobile station ( 102 ). In response to receiving the power down warning message and subsequently identifying the lost signal condition, the wireless network ( 104 ) causes network resources for the mobile station to be released. The wireless network ( 104 ) infers that the mobile station ( 102 ) has powered down due to low battery without enough time to send a power down registration to the wireless network ( 104 ).

BACKGROUND

1. Field of the Invention

The present invention relates generally to mobile stations operating ina wireless communication network, and more particularly to methods andapparatus for expeditiously releasing network resources for a mobilestation based on low battery and lost signal conditions.

2. Description of the Related Art

A wireless communication device, such as a mobile station operating in awireless communication network, may provide for both voice telephony anddata communications (e.g. IP packet data communications) for an enduser. A mobile station may, for example, be compatible with 3^(rd)Generation (3 G) communication standards (such as IS-2000 Release 0) andutilize Global System for Mobile Communications (GSM), Time DivisionMultiple Access (TDMA), or Code Division Multiple Access (CDMA) wirelessnetwork technologies.

Many mobile stations receive power from one or more batteries or batterypacks which are connected to the mobile stations. In current CDMA-basedwireless networks, at least some service providers require that a mobilestation automatically power itself off before its battery charge reachesan “empty” condition When a low battery condition is detected, themobile station performs a power down procedure which is similar to theprocess that occurs when the mobile station is manually powered off bythe end user. If the mobile station is in an “idle” state, the powerdown procedure includes generating an audible alert, sending a powerdown registration to the network on an access channel, and poweringitself off. If the mobile station is in a “dormant” packet data session,the mobile station is required to setup a data call merely to tear downa Point-to-Point Protocol (PPP) session established with the network,terminate the call, send the power down registration, and power itselfoff. If the mobile station is in an “active” traffic channel call, themobile station sends a release order message with power downregistration on the traffic channel and powers itself off. Somealternative methods are also possible and in general, these methods maybe referred to as conventional power down registration techniques.

The purpose of sending the power down registration before the mobilestation powers itself down is to conserve network resources. After thereceipt of the power down registration, the wireless network “knows”that the mobile station is unavailable and no longer requires servicefrom the network The wireless network knows, for example, that it isfutile to page the mobile station for incoming calls when it isunavailable. In addition, the wireless network may release networkresources such as an IP address and memory assigned to the mobilestation when the mobile station is unavailable. This includes, forexample, a Radio Access Network (RAN)-Packet Data Service Node (PDSN)binding or a Foreign Agent and Home Agent binding in a cdma2000™ network

When the mobile station is in an “active” traffic channel call, whichmay be a voice, data, or other type of call, it is not always possiblefor the mobile station to adequately transmit a release order messagewith power down registration before an actual hardware power failureoccurs due to the magnitude of the battery's voltage fluctuation. Givenwide current fluctuations, the mobile's battery voltage may drop acrossboth soft and hard “power-off” thresholds at nearly the same time andcause the transmitted signal to be lost. When the mobile station'sbattery condition becomes poor in an idle state or a dormant data packetsession, the mobile station may also experience a hardware power failurebefore it completes the power down procedure due to access probe ortraffic channel transmission activity.

The result may appear to the wireless network as a “call drop” due toreverse link fading. When this occurs, the wireless network does notexpeditiously release network resources for the mobile station. Over asubsequent time period during which the mobile station is inoperable andunavailable, the wireless network continues to page the unreachablemobile station for incoming communications and fails to deassign andreallocate its previously-assigned network resources.

Accordingly, what are needed are methods and apparatus for expeditiouslyreleasing network resources for a mobile station to overcome thedeficiencies in the prior art.

SUMMARY

Methods and apparatus for expeditiously releasing network resources fora mobile station based on low battery and lost signal conditions aredescribed herein. The wireless network receives a power down warningmessage from the mobile station indicative of a low battery conditionThe wireless network then identifies whether a lost signal conditionexists with the mobile station. In response to receiving the power downwarning message and identifing the lost signal condition, the wirelessnetwork causes network resources for the mobile station to be released.The wireless network infers that the mobile station has powered down dueto low battery without having enough time to successfully send a powerdown registration to the wireless network. Without use of techniquesdescribed herein, network resources for the mobile station remainallocated even though the mobile station is inoperable, which isinefficient and wasteful of network resources.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of present invention will now be described by way of examplewith reference to attached figures, wherein:

FIG. 1 is a block diagram which illustrates pertinent components of amobile station and a wireless communication network;

FIG. 2 is a more detailed diagram of a preferred mobile station of FIG.1;

FIG. 3 is a flowchart for describing a method of expeditiously releasingnetwork resources for a mobile station which is performed by the mobilestation; and

FIG. 4 is a flowchart for describing a method of expeditiously releasingnetwork resources for a mobile station which is performed by a wirelessnetwork component.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Methods and apparatus for expeditiously releasing network resources fora mobile station based on low battery and lost signal conditions aredescribed herein. The wireless network receives a power down warningmessage from the mobile station indicative of a low battery conditionThe wireless network then identifies whether a lost signal conditionexists with the mobile station. In response to receiving the power downwarning message and identifying the lost signal condition, the wirelessnetwork causes network resources for the mobile station to be released.The wireless network infers that the mobile station has powered down dueto low battery without enough time to successfully send a power downregistration to the wireless network. Without use of techniquesdescribed herein, network resources for the mobile station remainallocated even though the mobile station is inoperable, which isinefficient and wasteful of network resources.

FIG. 1 is a block diagram of a communication system 100, which includesa mobile station 102, which communicates through a wirelesscommunication network 104. Mobile station 102 preferably includes avisual display 112, a keyboard 114, and perhaps one or more auxiliaryuser interfaces (UI) 116, each of which is coupled to a controller 106.Controller 106 is also coupled to radio frequency (RF) transceivercircuitry 108 and an antenna 110. Typically, controller 106 is embodiedas a central processing unit (CPU), which runs operating system softwarein a memory component (not shown). Controller 106 will normally controloverall operation of mobile station 102, whereas signal-processingoperations associated with communication functions are typicallyperformed in RF transceiver circuitry 108. Controller 106 interfaceswith device display 112 to display received information, storedinformation, user inputs, and the like. Keyboard 114, which may be atelephone type keypad or full alphanumeric keyboard, is normallyprovided for entering data for storage in mobile station 102,information for transmission to network 104, a telephone number to placea telephone call, commands to be executed on mobile station 102, andpossibly other or different user inputs.

Mobile station 102 sends communication signals to and receivescommunication signals from network 104 over a wireless link via antenna110. RF transceiver circuitry 108 performs functions similar to those ofa radio network (RN) 128, including for example modulation/demodulationand possibly encoding/decoding and encryption/decryption. It is alsocontemplated that RF transceiver circuitry 108 may perform certainfunctions in addition to those performed by RN 128. It will be apparentto those skilled in art that RF transceiver circuitry 108 will beadapted to particular wireless network or networks in which mobilestation 102 is intended to operate.

Mobile station 102 includes a battery interface 122 for receiving one ormore rechargeable batteries 124. Battery 124 provides electrical powerto electrical circuitry in mobile station 102, and battery interface 122provides for a mechanical and electrical connection for battery 124.Battery interface 122 is coupled to a regulator 126 which regulatespower to the device, providing an output having a regulated voltage V.The output from battery interface 122 is further coupled to batterysensing circuitry 190 which helps monitor the condition of battery 124with controller 106. Mobile station 102 also operates using a memorymodule 120, such as a Subscriber Identity Module (SIM) or a RemovableUser Identity Module (R-UIM), which is connected to or inserted inmobile station 102 at an interface 118.

Mobile station 162 may consist of a single unit, such as a datacommunication device, a cellular telephone, a multiple-functioncommunication device with data and voice communication capabilities, apersonal digital assistant (PDA) enabled for wireless communication, ora computer incorporating an internal modem. Alternatively, mobilestation 102 may be a multiple-module unit comprising a plurality ofseparate components, including but in no way limited to a computer orother device connected to a wireless modem. In particular, for example,in the mobile station block diagram of FIG. 1, RF transceiver circuitry108 and antenna 110 may be implemented as a radio modem unit that may beinserted into a port on a laptop computer. In this case, the laptopcomputer would include display 112, keyboard 114, one or more auxiliaryUIs 116, and controller 106 embodied as the computer's CPU. It is alsocontemplated that a computer or other equipment not normally capable ofwireless communication may be adapted to connect to and effectivelyassume control of RF transceiver circuitry 108 and antenna 110 of asingle-unit device such as one of those described above. Such a mobilestation 102 may have a more particular implementation as described laterin relation to mobile station 202 of FIG. 2.

Mobile station 102 communicates in and through wireless communicationnetwork 104. In the embodiment of FIG. 1, wireless network 104 is aThird Generation (3G) supported network based on Code Division MultipleAccess (CDMA) technologies. In particular, wireless network 104 is acdma2000™ network which includes fixed network components coupled asshown in FIG. 1. Cdma2000™ is a trademark of the TelecommunicationsIndustry Association (TIA). Wireless network 104 of the cdma2000-typeincludes a Radio Network (RN) 128, a Mobile Switching Center (MSC) 130,a Signaling System 7 (SS7) network 140, a Home LocationRegister/Authentication Center (HLR/AC) 138, a Packet Data Serving Node(PDSN) 132, an IP network 134, and a Remote Authentication Dial-In UserService (RADIUS) server 136. SS7 network 140 is communicatively coupledto a network 142 (such as a Public Switched Telephone Network or PSTN),whereas IP network is communicatively coupled to a network 144 (such asthe Internet).

During operation, mobile station 102 communicates with RN 128, whichperforms functions such as call-setup, call processing, and mobilitymanagement. RN 128 includes a plurality of base station transceiversystems that provide wireless network coverage for a particular coveragearea commonly referred to as a “cell”. A given base station transceiversystem of RN 128, such as the one shown in FIG. 1, transmitscommunication signals to and receives communication signals from mobilestations within its cell. The base station transceiver system normallyperforms such functions as modulation and possibly encoding and/orencryption of signals to be transmitted to the mobile station inaccordance with particular, usually predetermined, communicationprotocols and parameters, under control of its controller. The basestation transceiver system similarly demodulates and possibly decodesand decrypts, if necessary, any communication signals received frommobile station 102 within its cell. Communication protocols andparameters may vary between different networks. For example, one networkmay employ a different modulation scheme and operate at differentfrequencies than other networks. The underlying services may also differbased on its particular protocol revision.

The wireless link shown in communication system 100 of FIG. 1 representsone or more different channels, typically different radio frequency (RF)channels, and associated protocols used between wireless network 104 andmobile station 102. An RF channel is a limited resource that must beconserved, typically due to limits in overall bandwidth and a limitedbattery power of mobile station 102. Those skilled in art willappreciate that a wireless network in actual practice may includehundreds of cells depending upon desired overall expanse of networkcoverage. All pertinent components may be connected by multiple switchesand routers (not shown), controlled by multiple network controllers.

For all mobile station's 102 registered with a network operator,permanent data (such as mobile station 102 user's profile) as well astemporary data (such as mobile station's 102 current location) arestored in a HLR/AC 138. In case of a voice call to mobile station 102,HLR/AC 138 is queried to determine the current location of mobilestation 102. A Visitor Location Register (VLR) of MSC 130 is responsiblefor a group of location areas and stores the data of those mobilestations that are currently in its area of responsibility. This includesparts of the permanent mobile station data that have been transmittedfrom HLR/AC 138 to the VLR for faster access. However, the VLR of MSC130 may also assign and store local data, such as temporaryidentifications. HLR/AC 138 also authenticates mobile station 102 onsystem access. In order to provide packet data services to mobilestation 102 in a cdma2000-based network, RN 128 communicates with PDSN132. PDSN 132 provides access to the Internet 144 (or intranets,Wireless Application Protocol (WAP) servers, etc.) through IP network134. PDSN 132 also provides foreign agent (FA) functionality in mobileIP networks as well as packet transport for virtual private networking.PDSN 132 has a range of IP addresses and performs IP address management,session maintenance, and optional caching. RADIUS server 136 isresponsible for performing functions related to authentication,authorization, and accounting (AAA) of packet data services, and may bereferred to as an AAA server.

Those skilled in art will appreciate that wireless network 104 may beconnected to other systems, possibly including other networks, notexplicitly shown in FIG. 1. A network will normally be transmitting atvery least some sort of paging and system information on an ongoingbasis, even if there is no actual packet data exchanged. Although thenetwork consists of many parts, these parts all work together to resultin certain behaviours at the wireless link.

FIG. 2 is a detailed block diagram of a preferred mobile station 202utilized in the present application. Mobile station 202 is preferably atwo-way communication device having at least voice and advanced datacommunication capabilities, including the capability to communicate withother computer systems. Depending on the functionality provided bymobile station 202, it may be referred to as a data messaging device, atwo-way pager, a cellular telephone with data messaging capabilities, awireless Internet appliance, or a data communication device (with orwithout telephony capabilities). Mobile station 202 may communicate withany one of a plurality of base station transceiver systems 200 withinits geographic coverage area.

Mobile station 202 will normally incorporate a communication subsystem211, which includes a receiver 212, a transmitter 214, and associatedcomponents, such as one or more (preferably embedded or internal)antenna elements 216 and 218, local oscillators (LOs) 213, and aprocessing module such as a digital signal processor (DSP) 220.Communication subsystem 211 is analogous to RF transceiver circuitry 108and antenna 110 shown in FIG. 1. As will be apparent to those skilled infield of communications, particular design of communication subsystem211 depends on the communication network in which mobile station 202 isintended to operate.

Mobile station 202 may send and receive communication signals over thenetwork after required network registration or activation procedureshave been completed. Signals received by antenna 216 through the networkare input to receiver 212, which may perform such common receiverfunctions as signal amplification, frequency down conversion, filtering,channel selection, and like, and in example shown in FIG. 2,analog-to-digital (A/D) conversion. A/D conversion of a received signalallows more complex communication functions such as demodulation anddecoding to be performed in DSP 220. In a similar manner, signals to betransmitted are processed, including modulation and encoding, forexample, by DSP 220. These DSP-processed signals are input totransmitter 214 for digital-to-analog (D/A) conversion, frequency upconversion, filtering, amplification and transmission over communicationnetwork via antenna 218. DSP 220 not only processes communicationsignals, but also provides for receiver and transmitter control. Forexample, the gains applied to communication signals in receiver 212 andtransmitter 214 may be adaptively controlled through automatic gaincontrol algorithms implemented in DSP 220.

Network access is associated with a subscriber or user of mobile station202, and therefore mobile station 202 requires a memory module 262, suchas a Subscriber Identity Module or “SIM” card or a Removable UserIdentity Module (R-UIM), to be inserted in or connected to an interface264 of mobile station 202 in order to operate in the network. Sincemobile station 202 is a mobile battery-powered device, it also includesa battery interface 254 for receiving one or more rechargeable batteries256. Such a battery 256 provides electrical power to most if not allelectrical circuitry in mobile station 202, and battery interface 254provides for a mechanical and electrical connection for it. Batteryinterface 254 is coupled to a regulator (not shown) which regulatespower to all of the circuitry, providing an output having a regulatedvoltage V. The output of the battery interface 254 is coupled to batterysensing circuitry 280 which helps monitor the condition of battery 256using a microprocessor 238.

Microprocessor 238, which is one implementation of controller 106 ofFIG. 1, controls overall operation of mobile station 202. This controlincludes network selection techniques of the present application.Communication functions, including at least data and voicecommunications, are performed through communication subsystem 211.Microprocessor 238 also interacts with additional device subsystems suchas a display 222, a flash memory 224, a random access memory (RAM) 226,auxiliary input/output (I/O) subsystems 228, a serial port 230, akeyboard 232, a speaker 234, a microphone 236, a short-rangecommunications subsystem 240, and any other device subsystems generallydesignated at 242. Some of the subsystems shown in FIG. 2 performcommunication-related functions, whereas other subsystems may provide“resident” or on-device functions. Notably, some subsystems, such askeyboard 232 and display 222, for example, may be used for bothcommunication-related functions, such as entering a text message fortransmission over a communication network, and device-resident functionssuch as a calculator or task list. Operating system software used bymicroprocessor 238 is preferably stored in a persistent store such asflash memory 224, which may alternatively be a read-only memory (ROM) orsimilar storage element (not shown). Those skilled in the art willappreciate that the operating system, specific device applications, orparts thereof, may be temporarily loaded into a volatile store such asRAM 226.

Microprocessor 238, in addition to its operating system functions,preferably enables execution of software applications on mobile station202. A predetermined set of applications, which control basic deviceoperations, including at least data and voice communicationapplications, will normally be installed on mobile station 202 duringits manufacture. A preferred application that may be loaded onto mobilestation 202 may be a personal information manager (PIM) applicationhaving the ability to organize and manage data items relating to usersuch as, but not limited to, e-mail, calendar events, voice mails,appointments, and task items. Naturally, one or more memory stores areavailable on mobile station 202 and SIM 256 to facilitate storage of PIMdata items and other information.

The PIM application preferably has the ability to send and receive dataitems via the wireless network. In a preferred embodiment, PIM dataitems are seamlessly integrated, synchronized, and updated via thewireless network, with the mobile station user's corresponding dataitems stored and/or associated with a host computer system therebycreating a mirrored host computer on mobile station 202 with respect tosuch items. This is especially advantageous where the host computersystem is the mobile station user's office computer system. Additionalapplications may also be loaded onto mobile station 202 through network,an auxiliary I/O subsystem 228, serial port 230, short-rangecommunications subsystem 240, or any other suitable subsystem 242, andinstalled by a user in RAM 226 or preferably a non-volatile store (notshown) for execution by microprocessor 238. Such flexibility inapplication installation increases the functionality of mobile station202 and may provide enhanced on-device functions, communication-relatedfunctions, or both. For example, secure communication applications mayenable electronic commerce functions and other such financialtransactions to be performed using mobile station 202.

In a data communication mode, a received signal such as a text message,an e-mail message, or web page download will be processed bycommunication subsystem 211 and input to microprocessor 238.Microprocessor 238 will preferably further process the signal for outputto display 222 or alternatively to auxiliary I/O device 228. A user ofmobile station 202 may also compose data items, such as e-mail messages,for example, using keyboard 232 in conjunction with display 222 andpossibly auxiliary I/O device 228. Keyboard 232 is preferably a completealphanumeric keyboard and/or telephone-type keypad. These composed itemsmay be transmitted over a communication network through communicationsubsystem 211.

For voice communications, the overall operation of mobile station 202 issubstantially similar, except that the received signals would be outputto speaker 234 and signals for transmission would be generated bymicrophone 236. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on mobilestation 202. Although voice or audio signal output is preferablyaccomplished primarily through speaker 234, display 222 may also be usedto provide an indication of the identity of a calling party, duration ofa voice call, or other voice call related information, as some examples.

Serial port 230 in FIG. 2 is normally implemented in a personal digitalassistant (PDA)-type communication device for which synchronization witha user's desktop computer is a desirable, albeit optional, component.Serial port 230 enables a user to set preferences through an externaldevice or software application and extends the capabilities of mobilestation 202 by providing for information or software downloads to mobilestation 202 other than through a wireless communication network. Thealternate download path may, for example, be used to load an encryptionkey onto mobile station 202 through a direct and thus reliable andtrusted connection to thereby provide secure device communication.

Short-range communications subsystem 240 of FIG. 2 is an additionaloptional component, which provides for communication between mobilestation 202 and different systems or devices, which need not necessarilybe similar devices. For example, subsystem 240 may include an infrareddevice and associated circuits and components, or a Bluetooth™communication module to provide for communication with similarly enabledsystems and devices. Bluetooth™ is a registered trademark of BluetoothSIG, Inc.

FIG. 3 is a flowchart for describing a method of expeditiously releasingnetwork resources for a mobile station. The method of FIG. 3 may beperformed by a mobile station, and is associated with the flowchart ofFIG. 4 which describes a method performed by the wireless network. Asdescribed in relation to FIGS. 1-2, the mobile station may include awireless transceiver, an antenna coupled to the wireless transceiver,one or more processors (e.g. a microprocessor and/or a DSP) havingsoftware instructions to perform the described method, a batteryinterface to provide coupling to one or more batteries which supplypower to the mobile station, and battery sensing circuitry coupled tothe battery interface and to the one or more processors to sense andreport battery condition. A computer program product may includecomputer instructions stored on a computer storage medium (memory, afloppy disk or CD-ROM), which are written in accordance with thedescribed logic.

Beginning at start block 302 of FIG. 3, a “PAT” timer is set to a zeroinitial value and disabled during an initialization procedure of themobile station (e.g. after powering on the mobile station). The PATtimer is a timer which, when enabled, defines a time duration over whicha power down warning remains valid in the wireless network. Duringoperation, the mobile station monitors signals through its batteryinterface to identify any special battery conditions (step 304). In thepresent embodiment, the mobile station monitors three different batteryconditions which are defined by three different thresholds A, B, and C,where A>B>C. The mobile station also monitors whether the PAT timer iszero (or close to zero) (step 306). If the PAT timer is not zero (norclose to zero) at step 306, the mobile station proceeds to step 308which will be described later below.

If the PAT timer is zero (or close to zero) at step 306, the mobilestation identifies whether a low battery condition exists whereA≧Battery Signal>B (step 312). If the low battery condition exists atstep 312, then the mobile station identifies whether one or more activeservices such as voice call or packet data call are being utilized bythe mobile station (step 314). If no active service is being utilized asidentified at step 314, then the mobile station continues to monitor thebattery condition at step 304. If one or more active services are beingutilized as identified at step 314, however, then the mobile stationcauses a control message for packet data rate reduction to betransmitted to the wireless network (step 316). Note that a lowertransmission data rate conserves battery power at the mobile station. Assome examples, the control message may cause a data rate for packet datacommunications to be reduced to 76.8 kbps from 153.6 kbps; or a datarate for voice communications to be reduced to 8 kbps from 13 kbps. Themessage may be sent only if the data rate is not reduced already or,alternatively, may be sent even if redundant to ensure that the datarate is kept low. The mobile station continues to monitor the batterycondition starting again in the flowchart at step 304.

Although not explicitly detailed in FIG. 3, the mobile station may alsosend a control message for an increase in the packet data rate when thebattery condition becomes acceptable (e.g. Battery Signal>A). Thispacket data rate increase adjusts the data rate for the one or morepacket data services to its originally intended data rate. Conditionsfor a packet data rate increase may occur, for example, after thebattery has been charged or the battery operating temperature becomesmore favorable. The wireless network may alternatively increase theallowable packet data rate in response to an expiration of time duringwhich no message for packet data rate reduction is received from themobile station. Note that, in the embodiment of FIGS. 3-4, steps 312,314 and 316 are optional.

Moving ahead in the flowchart of FIG. 3, if the low battery condition atstep 312 is not identified, the mobile station identifies whether adifferent low battery condition exists where B≧Battery Signal>C (step318). This low battery condition is more severe than that tested for instep 312. If such low battery condition is not identified in step 318,the mobile station proceeds to step 330 which will be described laterbelow. If such low battery condition does exist at step 318, however,then the mobile station identifies whether the PAT timer is zero (orclose to zero) (step 324). If the PAT timer is not zero (nor close tozero) at step 324, the mobile station continues monitoring the batterycondition again at step 304.

If the PAT timer is zero (or close to zero) at step 324, the mobilestation causes a control message to indicate a “power down warning” tobe transmitted to the wireless network (step 326). The power downwarning message is indicative of the low battery condition at the mobilestation. This control message of step 326 is typically sent as anin-traffic channel message to the wireless network if the mobile stationis involved in an on-going traffic call. Alternatively, the controlmessage is sent over an access channel, an enhanced access channel, or acommon control channel if there is no on-going traffic call involvingthe mobile station. The message may be in any suitable form and suitablynamed, for example, as a Power Down Warning message, a Low Battery Alertmessage, a Battery Status message which includes data identifying thelow battery condition, etc.

Regardless of the form or name, the power down warning message is usedfor causing the wireless network to release network resources for themobile station if a lost signal condition with the mobile station issubsequently identified. A lost signal condition may be detected by thewireless network in a number of different ways. During a traffic callfor the mobile station, a loss of the reverse link traffic signal over apersistent period of time (e.g. five seconds) is deemed to be a lostsignal condition. In an idle or dormant operational state of the mobilestation, no renewal or cancellation of the previous power down warningmessage being received within a predetermined time period is also deemedto be a lost signal condition.

The power down warning message is useful since the mobile station maypower down without sufficient time to successfully transmit aconventional power down registration or indication due to insufficientpower being received through its battery interface (i.e. a hardwarepower failure). Upon detecting a lost signal condition during a powerdown warning mode, the wireless network infers that the mobile stationhas unintentionally powered down due to low battery without adequatetime to successfully send the power down registration/indication. Whenthe wireless network causes network resources of the mobile station tobe released, the mobile station is no longer available from the wirelessnetwork's perspective. The wireless network refrains from paging themobile station when an incoming communication to the mobile station isreceived. Also, a previously-assigned IP address of the mobile stationis deassigned from the mobile station and reallocated into the existingpool of available IP addresses. Thereafter, the mobile station will berequired to send a power-up registration when it is back in operationwith a recharged, recovered, and/or replaced battery.

Upon sending the power down registration message in step 326, the mobilestation sets the PAT timer to a predetermined time period over which thecurrent power down warning is valid, and starts running this timer (step328). The value for the PAT timer may be included in a data field of thecontrol message for receipt and use by the wireless network.Alternatively, a predetermined PAT timer value known to both the networkand the mobile station may be used. Note that the mobile station willregularly cause a power down warning message to be sent to the wirelesscommunication network within the predetermined time period defined bythe PAT timer. Thus, this message may be a periodically or regularlytransmitted message from the mobile station. If the wireless networkdoes not receive a new or reissued power down warning message from themobile station within the time period defined by the PAT timer, then alost signal condition with the mobile station will be deemed to exist.

Note that the power down warning message should be transmitted to thewireless network slightly earlier than the expiration of the PAT timerso that it can arrive at and be processed by the network before itexpires on the network side. Thus, the test condition at step 324 is“Yes” when a small value (close to zero) is identified.

Continuing on with the flowchart of FIG. 3, if the PAT timer is not zero(nor close to zero) at step 306, then the mobile station tests whetherthe Battery Signal>B. If the Battery Signal>B at step 306, then thebattery of the mobile station has been recharged (or the temperature hasimproved) and therefore the mobile station sends a power down warningcancellation message to the wireless network (step 310). The warningcancellation message is for immediately canceling a previously-issuedpower down warning for the mobile station in the wireless network. Whenthe warning cancellation message is sent, the PAT timer is set to zeroand disabled at step 310. If the Battery Signal is ≦B as tested in step308, the method continues at step 312 as described earlier above.

Continuing at step 318, if the low battery condition is not identifiedat step 318 then the mobile station identifies whether a yet differentlow battery condition exists where Battery Signal≦C (step 330). This lowbattery condition is even more severe than that tested for in step 318.If such low battery condition does not exist as identified at step 330,then the mobile station continues monitoring the battery condition backat step 304. If such low battery condition exists as identified at step330, however, a power down procedure which includes the sending of apower down registration or indication to the wireless network isperformed (step 332).

Although the mobile station is supposed to transmit the conventionalpower down registration or indication in step 332 in response to the lowbattery condition at step 330, the mobile station may unintentionallypower down before it can transmit or adequately transmit such a messageto the wireless network. This is more likely to occur during a callinvolving the mobile station where the transmitter power is relativelyhigh. Even if transmitted, the power down registration may be unreliableduring the low battery condition. Thus, the power down warning messageof step 326 is particularly advantageous so that the wireless networkmay subsequently infer from a lost signal condition (e.g. lack of RFsignal or from timeout without renewal or cancellation of warning) thatthe mobile station has powered down due to low battery without enoughtime to adequately send the power down registration. In response, thewireless network expeditiously releases network resources associatedwith the mobile station. Otherwise, the network resources for the mobilestation remain allocated even though the mobile station is inoperable,which is inefficient and wasteful of network resources.

FIG. 4 is a flowchart for describing a related method of expeditiouslyreleasing network resources for a mobile station. The method of FIG. 4may be performed in a wireless network by a wireless network componentsuch as a network processor or server, and is associated with theflowchart of FIG. 3 which describes a method performed by the mobilestation. The wireless network component may include one or moreprocessors, memory, and computer instructions stored in the memory whichare executable by the one or more processors to perform the method. Acomputer program product may include computer instructions stored on acomputer storage medium (memory utilized by the one or more processors,a floppy disk or CD-ROM), which are written in accordance with thedescribed logic.

Beginning at a start block 402 of FIG. 4, the wireless network monitorsfor various conditions and messages received from a mobile station (step404). A test is performed to identify whether a control message for datarate reduction has been received from the mobile station (step 406). Ifthe message for data rate reduction has been received at step 406, thenthe wireless network causes a data rate for one or more packet dataservices utilized by the mobile station to be reduced (step 408). Notethat a lower data rate conserves battery power at the mobile station. Assome examples, the control message may cause a data rate for packet datacommunications to be reduced to 76.8 kbps from 153.6 kbps; or a datarate for voice communications to be reduced to 8 kbps from 13 kbps. Themessage may be received only if the data rate has not been reducedalready or, alternatively, may be received even if redundant (i.e.already received previously) to ensure that the data rate is kept low.

Note that, although not explicitly detailed in the flowchart of FIG. 4,the wireless network may also receive a control message for an increasein the packet data rate when the battery condition of the mobile stationbecomes acceptable. Alternatively, the wireless network may increase theallowable packet data rate after an expiration of timer during which nomessage for packet data rate reduction is received from the mobilestation. The packet data rate increase increases the data rate for theone or more packet data services to its originally intended data rate.

Moving ahead in FIG. 4, a test is performed to identify whether acontrol message which indicates a power down warning has been receivedfrom the mobile station (step 410). As previously described, the powerdown warning message is indicative of the low battery condition at themobile station and is typically sent as an in-traffic channel messageduring a traffic call. Alternatively, the power down warning message maybe sent over an access channel, an enhanced access channel, or a commoncontrol channel during an idle or dormant operating state of the mobilestation. The message may be in any suitable form and be suitably named,for example, as a Power Down Warning message, a Low Battery Alertmessage, a Battery Status message which includes data identifying thelow battery condition, etc. Regardless of the form or name, the powerdown warning message is used for causing the wireless network to releasenetwork resources for the mobile station if a lost signal conditionbetween the mobile station and the wireless network is subsequentlyidentified, as will be revealed in subsequent steps of FIG. 4.

If a power down warning message is received at step 410, then a powerdown warning mode for the mobile station is initiated by the wirelessnetwork (step 412). When this mode is initiated, a PAT timer is set to apredetermined value T which may be provided for in the power downwarning message from the mobile station. This PAT timer may be utilizedlater to test whether there is a lost signal condition with the mobilestation and the wireless network. Next, a test is performed to identifywhether a control message which indicates a power down warningcancellation has been received from the mobile station (step 414). Thispower down warning cancellation message is indicative of an improvedbattery condition at the mobile station. If the power down warningcancellation message has been received as identified at step 414, thenthe power down warning mode is terminated for the mobile station and thePAT timer is stopped (step 416).

Next, a test is performed to identify whether the mobile station is in apower down warning mode (step 418). If the mobile station is in thepower down warning mode at step 418, then a test is performed todetermine whether a lost signal condition exists between the mobilestation and the wireless network (step 420). If the lost signalcondition exists with the mobile station at step 420, then the wirelessnetwork causes network resources for the mobile station to be released(step 424). Note that in step 424 the wireless network performs all ofthose procedures necessary, conventional or otherwise, to releasenetwork resources for the mobile station as if the wireless network hasreceived a power down registration (or release order with power downindication) from the mobile station.

The test of step 420 may be performed in a few different ways dependingon the operational mode of the mobile station. During traffic channeluse, the lost signal condition may be based on a loss of RF signaland/or data communication over a predetermined period of time. If thesignal or data communication is lost only for less than thepredetermined time period, then no lost signal condition exists;conversely, if the signal or data communication is lost continuouslyover the predetermined time period or greater, then the lost signalcondition exists. The predetermined period of time may be, for example,five (5) seconds which is a typical fade time. However, any suitabletime period may be utilized. If the time period established is tooshort, the wireless network may incorrectly infer that the mobilestation has powered down despite it merely going through a shorttemporary fade. If the time period established is too long, the wirelessnetwork will not release network resources for the mobile station asexpeditiously as it should.

During idle mode operation or a dormant data session, the lost signalcondition of step 420 may be determined by identifying whether a new orreissued power down warning message has been received from the mobilestation by the wireless network within the time period defined by thePAT timer. If the time period defined by PAT timer expires before a newor reissued power down warning message has been received, then a lostsignal condition with the mobile station is identified to exist. Whenconditions are normal, the PAT timer is reset to its default value eachtime a power down warning message is received from the mobile station.

If no power down warning mode is being maintained in step 418, or nolost signal condition exists at step 420, then the wireless networkidentifies whether a conventional power down registration or indicationmessage has been received from the mobile station (step 422). If thepower down registration message has been received at step 422, then thewireless network causes network resources for the mobile station to bereleased (step 424). The wireless network performs all of thoseprocedures necessary, conventional or otherwise, to release networkresources for the mobile station in response to the power downregistration from the mobile station. When the wireless network causesnetwork resources of the mobile station to be released, the mobilestation is no longer available from the wireless network's perspective.The wireless network refrains from paging the mobile station when anincoming communication to the mobile station is received. Also, apreviously-assigned IP address of the mobile station is deassigned fromthe mobile station and reallocated into the existing pool of availableIP addresses.

Thus, although the wireless network is supposed to receive a power downregistration in step 422 from the mobile station when it identifies asevere low battery condition, the mobile station may unintentionallypower down before it can successfully transmit such a message. This mayoccur during a call or during transmission of the power downregistration where the mobile station transmitter power is high enoughso as to cause undesirable battery signal variations. It is for thatsituation the power down warning message at step 410 is particularlyadvantageous, so that the wireless network may subsequently infer from alost signal condition that the mobile station has powered down due tolow battery without successfully transmitting the power downregistration/indication. In response, the wireless network expeditiouslyreleases network resources associated with the mobile station.Otherwise, the network resources for the mobile station remain allocatedeven though the mobile station is inoperable, which is inefficient andwasteful of network resources.

In an alternate embodiment, a PAT timer is not utilized. This is adegenerated special case where the PAT timer may be viewed as having avalue of infinity. In this case, the sending of the power down warningmessage is performed only when there is an active traffic channel forthe mobile station, and the detection of a lost signal condition isbased on a loss of the reverse link traffic signal over a persistentperiod of time (e.g. five seconds) without a normal release order beingreceived. In another alternate embodiment, the PAT timers at both themobile station and the wireless network are reset to the default valuewhenever there is any acknowledged signaling exchange between the mobilestation and the wireless network, if the PAT timer has not expired.

Methods and apparatus for expeditiously releasing network resources fora mobile station based on low battery and lost signal conditions havebeen described. The wireless network receives a power down warningmessage from the mobile station indicative of a low battery condition.The wireless network then identifies whether a lost signal conditionexists with the mobile station. In response to receiving the power downwarning message and identifying the lost signal condition, the wirelessnetwork causes network resources for the mobile station to be released.The wireless network infers that the mobile station has powered down dueto low battery without enough time to send a power down registration tothe wireless network Without use of techniques described herein, networkresources for the mobile station remain allocated even though the mobilestation is inoperable, which is inefficient and wasteful. In the mobilestation, the method involves identifying whether a low battery conditionexists. In response to identifying the low battery condition, the mobilestation causes a power down warning message indicative of the lowbattery condition to be sent to the wireless communication network. Thepower down warning message is used for causing the wirelesscommunication network to release network resources for the mobilestation when a lost signal condition between the mobile station and thewireless communication network subsequently occurs.

The above-described embodiments of the present application are intendedto be examples only. Those of skill in the art may effect alterations,modifications and variations to the particular embodiments withoutdeparting from the scope of the application. The invention describedherein in the recited claims intends to cover and embrace all suitablechanges in technology.

1. In a wireless communication network, a method of expeditiouslyreleasing network resources for a mobile station comprising the acts of:receiving, from a mobile station, a message indicative of a low batterycondition of the mobile station; identifying that a lost signalcondition exists between the mobile station and the wirelesscommunication network; failing to receive a power down registrationmessage from the mobile station; and despite the failure to receive thepower down registration message from the mobile station, performing aresponse to a power down registration for the mobile station in responseto receiving the message indicative of the low battery condition andidentifying the lost signal condition, to thereby cause one or morenetwork resources for the mobile station to be released.
 2. The methodof claim 1, further comprising: determining that the mobile station hasshut down based on receiving the message indicative of the low batterycondition and identifying the lost signal condition.
 3. The method ofclaim 1, wherein causing the network resource to be released comprisesrefraining from paging the mobile station when an incoming communicationto the mobile station is received in the wireless communication network.4. The method of claim 1, wherein causing the network resource to bereleased comprises deassigning a previously-assigned IP address for themobile station.
 5. The method of claim 1, wherein the message indicativeof the low battery condition includes a timer value which defines a timeduration over which a power down warning indicated by the power downwarning message is valid in the wireless communication network.
 6. Themethod of claim 1, wherein the act of identifying that the lost signalcondition exists comprises identifying that the lost signal conditionexists for a predetermined time period.
 7. The method of claim 1,wherein the act of identifying that the lost signal condition existscomprises identifying that a loss of radio frequency (RF) signal betweenthe mobile station and the wireless communication network exists.
 8. Themethod of claim 1, wherein the act of identifying that the lost signalcondition exists comprises identifying that a loss of data communicationwith the mobile station exists.
 9. The method of claim 1, wherein theact of identifying that the lost signal condition exists comprises:running a timer; and identifying the lost signal condition upon failureto receive a regularly transmitted message from the mobile stationwithin predetermined time period defined by the timer.
 10. The method ofclaim 1, wherein the act of receiving the message indicative of the lowbattery condition comprises receiving the message while a trafficchannel is established between the mobile station and the wirelesscommunication network, the message comprising an in-traffic channelmessage.
 11. The method of claim 1, wherein the act of receiving themessage indicative of the low battery condition comprises receiving themessage over one of an access channel and a common control channel. 12.A wireless network component for use in a wireless communicationnetwork, comprising: one or more processors; memory; computerinstructions stored in the memory; the computer instructions beingexecutable by the one or more processors for: receiving, from a mobilestation, a message indicative of a low battery condition of the mobilestation; identifying that a lost signal condition exists between themobile station and the wireless communication network; and failing toreceive a power down registration message from the mobile station; andperforming a response to a power down registration for the mobilestation in response to receiving the message indicative of the lowbattery condition and identifying the lost signal condition, to therebycause one or more network resources for the mobile station to bereleased.
 13. The wireless network component of claim 12, wherein thecomputer instructions are further executable by the one or moreprocessors for: determining that the mobile station has powered down inresponse to receiving the message indicative of the low batterycondition and identifying the lost signal condition.
 14. The wirelessnetwork component of claim 12, wherein causing the network resource tobe released comprises refraining from paging the mobile station when anincoming communication to the mobile station is received in the wirelesscommunication network.
 15. The wireless network component of claim 12,wherein causing the network resource to be released comprisesdeassigning a previously-assigned IP address for the mobile station. 16.The wireless network component of claim 12, wherein the messageindicative of the low battery condition includes a timer value whichdefines a time duration over which a power down warning indicated by themessage is valid in the wireless communication network.
 17. The wirelessnetwork component of claim 12, wherein identifying that the lost signalcondition exists comprises identifying that the lost signal conditionexists for a predetermined time period.
 18. The wireless networkcomponent of claim 12, wherein identifying that the lost signalcondition exists comprises identifying that a loss of radio frequency(RF) signal between the mobile station and the wireless communicationnetwork exists.
 19. The wireless network component of claim 12, whereinidentifying that the lost signal condition exists comprises identifyingthat a loss of data communication with the mobile station exists. 20.The wireless network component of claim 12, wherein identifying that thelost signal condition exists comprises running a timer; and identifyingthe lost signal condition upon failure to receive a regularlytransmitted message from the mobile station within a predetermined timeperiod defined by the timer.
 21. The wireless network component of claim12, wherein receiving the message indicative of the low batterycondition comprises receiving the message while a traffic channel isestablished between the mobile station and the wireless communicationnetwork, the message comprising an in-traffic channel message.
 22. Thewireless network component of claim 12, wherein receiving the messageindicative of the low battery condition comprises receiving the messageover one of an access channel and a common control channel.
 23. In amobile station, a method of expeditiously releasing network resources ina wireless communication network comprising: identifying that a lowbattery condition exists; in response to identifying the low batterycondition, causing a message indicative of the low battery condition tobe sent to the wireless communication network; after causing the messageindicative of the low battery condition to be sent, receivinginsufficient power through a battery interface of the mobile station soas to unintentionally power down without sufficient time to cause apower down registration message to be sent to the wireless communicationnetwork; and wherein the message indicative of the low battery conditionindicates to the wireless communication network to perform a power downregistration for the mobile station when a lost signal condition for themobile station is identified despite a failure of the wirelesscommunication network to receive the power down registration messagefrom the mobile station.
 24. The method of claim 23, wherein theincludes a timer value which defines a time duration over which a powerdown warning indicated by the message is valid in the wirelesscommunication network.
 25. The method of claim 23, further comprising:regularly causing the message indicative of the low battery condition tobe sent to the wireless communication network within a predeterminedtime period.
 26. The method of claim 23, wherein the message indicativeof the low battery condition further indicates to the wirelesscommunication network to refrain from paging the mobile station when anincoming communication to the mobile station is received in the wirelesscommunication network.
 27. The method of claim 23, wherein the messageindicative of the low battery condition comprises an in-traffic channelmessage.
 28. The method of claim 23, wherein causing the messageindicative of the low battery condition to be sent comprises causing themessage to be sent while a traffic channel is established between themobile station and the wireless communication network.
 29. The method ofclaim 23, wherein the message indicative of the low battery condition issent over one of an access channel and a common control channel.
 30. Themethod of claim 23, wherein the message indicative of the low batterycondition further indicates to the wireless communication network todeassign a previously-assigned IP address for the mobile station. 31.The method of claim 23, wherein the low battery condition comprises afirst low battery condition, the method further comprising: identifyingthat a second low battery condition exists; and in response toidentifying the second low battery condition, causing a packet data ratereduction message to be sent to the wireless communication network. 32.The method of claim 23, wherein the low battery condition comprises afirst low battery condition, the method further comprising: identifyingthat a second low battery condition exists; and in response toidentifying the second low battery condition, causing a power downprocedure to be performed which includes sending a power downregistration or indication to the wireless communication network.
 33. Amobile station, comprising: a wireless transceiver; an antenna coupledto the wireless transceiver; one or more processors coupled to thewireless transceiver; a battery interface to provide coupling to one ormore batteries which supply power to the mobile station; battery sensingcircuitry coupled to the battery interface; the one or more processorsbeing operative to: identify that a low battery condition exists; inresponse to identifying the low battery condition, cause a messageindicative of the low battery condition to be sent through the wirelesstransceiver to the wireless communication network; after causing themessage indicative of the low battery condition to be sent, receiveinsufficient power through the battery interface so as tounintentionally power down without sufficient time to cause a power downregistration message to be sent through the wireless transceiver to thewireless communication network; and wherein the message indicative ofthe low battery condition indicates to the wireless communicationnetwork to perform a power down registration for the mobile station whena lost signal condition for the mobile station is identified despite afailure of the wireless communication network to receive the power downregistration message from the mobile station.
 34. The mobile station ofclaim 33, wherein the message indicative of the low battery conditionincludes a timer value which defines a time duration over which a powerdown warning indicated by the message is valid in the wirelesscommunication network.
 35. The mobile station of claim 33, wherein theone or more processors are further operative to regularly causing causethe message indicative of the low battery condition to be sent to thewireless communication network within a predetermined time period. 36.The mobile station of claim 33, wherein the message indicative of thelow battery condition further causes the wireless communication networkto refrain from paging the mobile station when an incoming communicationto the mobile station is received in the wireless communication network.37. The mobile station of claim 33, wherein the message indicative ofthe low battery condition comprises an in-traffic channel message. 38.The mobile station of claim 33, wherein causing the message indicativeof the low battery condition to be sent comprises causing the message tobe sent while a traffic channel is established between the mobilestation and the wireless communication network.
 39. The mobile stationof claim 33, wherein the message indicative of the low battery conditionis transmitted over one of an access channel and a common controlchannel.
 40. The mobile station of claim 33, wherein the messageindicative of the low battery condition further indicates to thewireless communication network to deassign a previously-assigned IPaddress for the mobile station.
 41. The mobile station of claim 33,wherein the low battery condition comprises a first low batterycondition, the one or more processors being further operative to:identify that a second low battery condition exists; and in response toidentifying the second low battery condition, cause a packet data ratereduction message to be sent to the wireless communication network. 42.The mobile station of claim 33, wherein the low battery conditioncomprises a first low battery condition, the one or more processorsbeing further operative to: identify that a second low battery conditionexists; and in response to identifying the second low battery condition,cause a power down procedure to be performed which includes sending apower down registration to the wireless communication network.